1. Field of the Invention
This invention relates to locking devices for threaded fasteners and, more particularly, to lock washers having one cam surface and an oppositely disposed friction surface.
2. Description of the Prior Art
As is well known in the art, various problems and difficulties are encountered in providing suitable means for locking devices to cooperate with fastener means such as the typical bolt-and-nut fastener.
A particular problem arises when a locking device is employed against a very hard surfaced material -- and, further, where such material must not be damaged by scratches or abrasions. Thus, known locking devices have not been able to overcome such problems.
In general, the locking devices known in the existing art are as follows:
1. A pair of identical annular lock washers, each having a cam face on one side and a friction face with radial extended teeth on the opposite side. The rise or pitch of the cams per degree of rotation is made greater than the rise of the threads of the fastener. The washer pair is installed cam-face to cam-face on a bolt-and-nut type fastener between the nut and the joint material, or between the head of a cap screw and the joint material.
2. A cap screw having the cam configuration described above formed into the underside of its head member, in order to interact directly with the cams of a single washer in the same manner as previously described.
3. A nut having a cam surface similar to that as described for the underside of the bolt head.
The above types of locking devices can be found in the following U.S. Pat. Nos:
3,895,663, John D. Bashline, et al;
3,263,727, Herpolsheimer;
3,329,190, Oldenkott;
743,822, Bryar.
The locking devices as above described are intended to function in the following manner: When the fastener is tightened, the washer adjacent the nut becomes fixed to the nut in a non-rotatable position due to the friction or embedding of the teeth in the surface of the nut. Likewise, the outer washer becomes fixed in a non-rotatable position to the surface of the joint material.
Thus, if a nut subjected to vibrational conditions attempts to rotate in the loosening direction, the mating washer is forced to "climb" the cams of the interacting washer that is fixed to the joint material, thereby increasing the initial clamping load and preventing the further loosening of the fastener.
However, under various conditions, the existing designs of the above-described locking devices do not offer positive and secure locking means for fasteners; and this has limited their acceptance and use thereof.
One type of installation where existing designs may not provide secure locking is where the surface of the joint material is smooth and harder than the teeth on the adjacent washer. The teeth then will not make any impact (become embedded) in the joint material; and only plain friction is provided to hold the washer and prevent it from rotating on the joint material when subjected to loosening forces.
Further, it is to be noted that existing designs of lock washers have cams as well as the teeth which are arranged to extend substantially the full width of the washer surface -- that is, from the central hole extending radially and outwardly therefrom, and terminating at the outer periphery thereof.